The invention relates to an apparatus and a method for optically projecting pixel-based image information onto a light-sensitive material. An apparatus of the kind that the invention seeks to improve has a device for generating partial images, an optical projection device, and a device for laterally offsetting the projection of the image-generating device to produce the partial images in the plane of the light-sensitive material. In a method of the kind that the invention seeks to improve, partial images of the pixel-based information are produced with an appropriate image-generating device. The projection of the image-generating device is moved in the lateral directions to produce the partial images in the plane of the light-sensitive material.
When producing an image of graphic information on a light-sensitive material, the aim is to maximize the detail resolution of the image. This is of particular importance in cases where the image-generating device is based on an electronic working principle. In electronic image-generating devices, the graphic information is generated as an assembly of individual pixels, where each pixel is represented by an individually controllable indicating element or elementary image component. However, image-generating devices based on this concept that are within a reasonable cost range have a resolution that is not adequate for producing images with a fine resolution at the quality level of photographs.
Thus, if the image information represented on an LCD (liquid crystal device), a DMD (digital mirror device) or another light modulator is to be projected onto a light-sensitive material such as a photographic paper, there are known methods of increasing the image resolution by using sequential projections of partial images. For example, to achieve a fourfold increase in resolution, only a fourth of the image data assigned to an LCD element of the image-generating device are processed in a first exposure, while the other three fourths of the LCD element are covered by a mask. In a second exposure, the projection of the LCD is moved, so that a second one-fourth of the total image information can be projected onto areas that were not previously exposed, and so on, continuing with a third and fourth exposure. After four exposures, each representing one-fourth of the total image information, a reproduction of the image is obtained with four times the resolution of the LCD array.
A method of generating a digital image is known from EP 0 987 875, where in essence an LCD device is projected onto an image carrier by means of an objective lens. A rotatable glass plate is used to produce a lateral offset of the projected pixels in the image plane, and the image carrier is exposed either once or more than once for each position of the projected image.
In order to set the glass plate into the correct position for each exposure, it is necessary to always know the current position. However, this requires a sensor arrangement with a very high resolution and a commensurately complex means of processing the sensor signals. Even with the use of expensive components, the accuracy and speed of positioning continue to be a problem.